On January 3, 2017, the FAA issued a Notice of Proposed Rulemaking (NPRM), prompted by reports of “fatigue cracking in the FS 332.00 bulkhead common to the horizontal stabilizer front spar attachment” of certain Piper Navajo aircraft models. The cracks in the bulkhead could “compromise the structural component’s capability to carry flight loads, increasing the potential to overload and fail adjacent structure.” The FAA has now issued an airworthiness directive (AD 2017-10-20) in order to facilitate the detection and repair of those bulkhead cracks, to prevent them from leading to a potential structural failure of the aircraft, and loss of control. In addition, in the case no cracks are found, the AD provides an optional modification that will greatly reduce the likelihood of the cracks developing.
The AD applies to the following Piper Navajo aircraft models, certificated in any category:
In addition, the FAA notes that though the PA-31 may also be identified as a PA-31-310, that PA-31-310 is not a model recognized on the type certificate data sheet.
As of the effective date of the AD (June 29, 2017), airplanes with 3,000 hours or less time-in-service (TIS) need to:
For airplanes with over 3,000 TIS:
For the inspection process, the FAA says to follow the instructions in Part 1 of Piper Aircraft’s Service Bulletin (SB) No. 1289A, which they issued on October 26, 2016.
If cracks are found, they will need to be repaired in accordance with the information found in AD 2017-10-20, and Piper SB 1289A. If no cracks are found, Piper Kit 88578-001 Revision B can be installed on an uncracked bulkhead following the Modification instructions provided in Piper SB 1289A. Once an acceptable repair or preventative action has been taken, it is considered a “terminating action” for the repetitive inspection requirement of the AD.
The FAA estimates that the AD will affect 955 airplanes on the US registry, and estimates the following costs for complying with the AD:
|Action||Labor cost||Parts cost||Cost per product||Cost on U.S. operators|
|Inspect for cracks in the bulkhead||12 work-hours × $85 per hour = $1,020||Not Applicable||$1020.00||$974,100|
If cracks are found during the inspections, the FAA estimates the cost of the necessary repairs to be:
|Action||Labor cost||Parts cost||Cost per product|
|Repair/Modification||45 work-hours × $85 per hour = $3,825||$296||$4,121|
The FAA notes that they have no way of determining how many of the airplanes the AD affects will need the repairs or replacements.
After issuing the NPRM, the FAA received a number of comments, which they addressed in the AD, one of which resulted in a change to the AD. Joe Miller, the Chief Inspector for Warbelow’s Air Ventures in Fairbanks, AK, said that after complying with the proposed requirements on 3 airplanes, they found that it took two mechanics about 6 hours each to accomplish the inspection phase, and further, that it took 2 mechanics about 4 days (or 64 total hours), to accomplish the complete process from inspection to returning the aircraft to service. Though the FAA’s original time estimate was provided by an experienced operator, the agency agreed to update their time estimates based on this new input:
For anyone interested in additional information regarding AD 2017-10-20, you can contact FAA Aerospace Engineer Gregory “Keith” Noles:
And for anyone seeking more information on the Piper service bulletin, you can contact Piper Aircraft customer service at:
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